1. Field of the Invention
The present invention relates to a susceptor with a built-in electrode and a manufacturing method therefor. In particular, the invention relates to a susceptor with a built-in electrode that has excellent corrosion resistance and plasma resistance and has an excellent durability to repeated rising and falling of the temperature, that is, the stress due to heat cycles, and a manufacturing method for a susceptor with a built-in electrode that enables the susceptor to be manufactured economically.
2. Description of the Related Art
In recent years, a manufacturing process called a xe2x80x9csingle plate processingxe2x80x9d that is, a manufacturing process plate by plate, is attracting attention in the field of manufacturing semiconductor devices such as ICs, LSIs and VLSIs because only the single plate processing ensures the reliable and uniform film deposition and etching in deposition systems such as a plasma etching apparatus, plasma CVD apparatus on plate specimens such as semiconductor wafers, glass plates as liquid crystal substrate, printing boards or the like. In this plate by plate processing, in order to process plate substrates one by one in a processing room, the plate specimens are mounted on a specimen support (pedestal) called a susceptor, and predetermined processing is carried out.
Because the susceptor must withstand for use within plasma atmosphere and for use in high temperature atmosphere, the susceptor must have excellent durability against exposure of plasma (plasma resistance) and high heat conductivity. For such a susceptor, a susceptor formed by an aluminum oxide sintered body exhibits excellent plasma resistance, thermal conductivity and heat resistance.
A particular type of susceptor is provided which comprises an internal electrode for use as a plasma generating electrode for generating plasma by supplying high-frequency electric power, as an electrostatic chucking electrode for chucking a plate specimen by an electrostatic attractive force originated by generated electric charge, or as a heater electrode for heating a plate specimen by resistive heating.
Conventionally, a structure shown in FIG. 3 is known as an example of a susceptor with a built-in electrode, formed by aluminum oxide based sintered body.
As shown in FIG. 3, a susceptor with a built-in electrode 5 (a susceptor with an internal electrode 2, which serves as a plasma generation electrode, is shown as an example) comprises: a mounting plate 1 for mounting a plate specimen; a support plate for supporting the mounting plate 1; an internal electrode 2 formed between the mounting plate 1 and the support plate 3; and a power supply terminal 4, which is embedded in the support plate 3 so as to be in contact with the internal electrode 2, and which supplies current to the internal electrode 2.
The mounting plate 1 is a flat body formed by a nonconductive aluminum oxide based sintered body, the support plate 3 is a flat substrate formed by a nonconductive aluminum oxide based sintered body, and the internal electrode 2 is constituted containing high melting point metals such as tungsten, molybdenum, tantalum, niobium or the like.
However, such a susceptor with a built-in electrode using an aluminum oxide based sintered body cannot withstand the stress of heat cycles (for example, repeated cycles of rising and falling temperature when the internal electrode 2 is used as a heater electrode, or the abnormal heating by the internal electrode when the internal electrode 2 is used as a plasma generation electrode), due to thermal stress caused by the difference in thermal expansion coefficients between the aluminum oxide based sintered body and the high melting point metal such as tungsten, molybdenum, tantalum, niobium or the like. Therefore, the problem arises in that conventional susceptor is cracked easily, durability is not sufficient, and cost is also high.
In order to solve the aforementioned problems, an object of the present invention is to provide a susceptor with a built-in electrode, which has not only excellent corrosion resistance, heat resistance and plasma resistance, but also has excellent durability for the aforementioned heat cycle stress, and to also provide a manufacturing method for a susceptor with a built-in electrode that allows producing such a susceptor with a built-in electrode at reduced cost.
As a result of intensive research into solving the above problems, the inventors discovered that by forming an internal electrode using a conductive material having a special composition inside the susceptor substrate made of an aluminum oxide based sintered body (in the present specification, xe2x80x9caluminum oxide based sintered bodyxe2x80x9d refers to not only an aluminum oxide sintered body, but also general aluminum oxide sintered body that contains aluminum oxide and other components such as silicon carbide, silica or the like at a ratio of less than 50 wt %, preferably less than 20 wt %), the above problems can be solved effectively and the present invention has been attained.
A susceptor with a built-in electrode according to a first aspect of the present invention comprises; a susceptor substrate made of an aluminum oxide based sintered body, an internal electrode, that is sealed in the susceptor substrate, and a power supply terminal that is embedded in the substrate in a state contacting with the internal electrode, wherein the internal electrode is formed by an aluminum oxide and molybdenum carbide based composite sintered body containing 30 to 95 volume % of molybdenum carbide and 5 to 70 volume % of aluminum oxide.
According to the second aspect of the present invention, in the above susceptor with a built-in electrode, said susceptor substrate comprises a first substrate formed by an aluminum oxide based sintered body and a second substrate formed by an aluminum oxide based sintered body, which is joined and unified with said first substrate.
According to the third aspect of the present invention, in the above susceptor with a built-in electrode, in the above susceptor with a built-in electrode, an insulating material layer comprising insulating material that has the same composition or the same principal component as the material constituting said first substrate and said second substrate is formed in a region excluding a part where said internal electrode is formed, so as to seal the internal electrode between the first substrate and the second electrode.
According to the fourth aspect of the present invention, in the above susceptor with a built-in electrode, said power supply terminal is formed by any one of an aluminum oxide and molybdenum carbide based composite sintered body, an aluminum oxide and tantalum carbide based composite sintered body, an aluminum oxide and tungsten based composite sintered body, and an aluminum oxide and silicon carbide based composite sintered body.
In the susceptor with a built-in electrode with the construction described in the first to fourth aspects, since the internal electrode is formed by composite sintered body based on the aluminum oxide, and since the thermal stress caused by the difference between the coefficients of thermal expansion of the aluminum oxide based sintered body and the internal electrode is reduced, no cracking due to repeated rising and falling of the temperature (in other words, due to the heat cycles stress) occurs, the thermal durability of the susceptor is improved significantly. Furthermore, in contrast to the conventional susceptor in which the first substrate and the second substrate is not sealed using the insulating layer, since the susceptor with the built-in electrode according to the present invention is formed by sealing the internal electrode between the first and second substrates by use of the insulating layer, no corrosive gas or plasma penetrates the interface between the first plate and the second plate, and the internal electrode is not likely to be exposed to the corrosive gas or plasma, the susceptor exhibits excellent corrosion resistance and plasma resistance.
A manufacturing method for a susceptor with a built-in electrode according to a fifth aspect of the present invention comprises the steps of: forming a hole in a second substrate formed by an aluminum oxide based sintered body so as to pass through the substrate; fixing a power supply terminal into this hole; then coating the second substrate holding the power supply terminal, with a coating material containing an aluminum oxide and molybdenum carbide based composite material (in the present specification, xe2x80x9caluminum oxide with molybdenum carbide based composite materialxe2x80x9d also refers to a mixture of aluminum oxide and molybdenum carbide) containing 30 to 95 volume % of molybdenum carbide and 5 to 70 volume % of aluminum oxide, so as to make contact with the power supply terminal; drying; superposing the second substrate onto a first substrate formed from an aluminum oxide based sintered body so as to enclose the surface coated with the coating material; and heat treating under pressure, to thereby join and unify them, and also to form an internal electrode comprising an aluminum oxide and molybdenum carbide based composite sintered body between the first substrate and the second substrate.
In a manufacturing method for a susceptor with a built-in electrode with such a construction, since the already sintered mounting plate and the support plate can be heat treated together and joined and unified, it is easily possible to obtain a susceptor with a built-in internal electrode that has excellent corrosion resistance and plasma resistance, that withstands the stress of heat cycles, and that has excellent durability without causing cracks. Furthermore, since expensive niobium or tantalum are not needed to use, it is possible to manufacture a susceptor with a built-in internal electrode at reduced cost and at high production yield.
Moreover, a manufacturing method for a susceptor with a built-in electrode according to a sixth aspect of the present invention comprises the steps of: forming a first green body and a second green body that serve after sintering as a first substrate and a second substrate respectively; forming a hole in this second green body; fixing a power supply terminal into this hole so as to pass through the second green body; then coating the green body holding the power supply terminal, with a coating material containing an aluminum oxide and molybdenum carbide based composite material containing 30 to 95 volume % of molybdenum carbide and 5 to 70 volume % of aluminum oxide, so as to make contact with the power supply terminal, and drying it; then superposing the second green body onto the first green body so as to enclose the surface coated with the coating material; and heat treating under pressure and sintering, thereby forming a first substrate and a second substrate, which are joined and unified, and also forming an internal electrode comprising an aluminum oxide and molybdenum carbide based composite sintered body between the first and second substrates.
In a manufacturing method for a susceptor with a built-in electrode with such a construction, since the first and the second green bodies can be joined and unified, and also heat treated, it is easily possible by one heat treatment to obtain a susceptor with a built-in internal electrode that has excellent corrosion resistance and plasma resistance, that withstands the stress of heat cycles, and that has excellent durability without causing cracks. Furthermore, since expensive niobium or tantalum are not needed to use, it is possible to manufacture a susceptor with a built-in internal electrode at reduced cost and at high production yield.